Redundant Ignition Control Circuit and Method

ABSTRACT

A redundant ignition control system and method for gas burning appliances is provided. The system utilizes a main processor and a supervisory processor to provide the redundant, fail safe operation of both the pilot valve and the main gas valve of the appliance. Three switching elements under the control of the two processors, as well as the use of high pass filters to block DC from the gas control valves provide redundant, fail safe operation. The use of variable duty cycle or frequency pulse width modulated signals enables use in low power applications and ensures system safety. Inclusion of a gas valve verification sequence, ignition sequence, burner monitoring sequence, and heat shutdown and standby sequences ensures safe, low power operation during normal control, and fail safe operation upon the failure of any component of the system.

FIELD OF THE INVENTION

This invention generally relates to ignition control systems for intermittent pilot and direct spark ignition systems for gas burners, and more particularly to fail safe ignition control systems for such intermittent pilot and direct spark ignition systems enabling use of low power or self-powered sources.

BACKGROUND OF THE INVENTION

Ignition control systems, such as those used in controlling the flow of gas to a pilot burner and a main burner for gas fired water heaters, space heaters and furnaces are increasingly utilizing intermittent pilot or direct spark ignition systems, which do not use a standing pilot. These intermittent pilots most commonly use a flame sensing circuit to detect the presence of a flame before allowing the opening of the main gas valve that supplies the main burner to avoid unconsumed fuels from flowing freely.

As more and more applications are relying on low power sources, such as battery power or self-powered implementations via a thermopile or hydro generator, the energy consumption of typical ignition control systems becomes a serious design issue. These ignition control systems are typically required to control both the pilot valve and the main gas valve, and to do so in a safe manner. Unfortunately, the control methods used by these typical ignition control systems to energize and hold open these valves during the entire call for heat event is not compatible with newer lower voltage supplies. This power problem is further compounded when failsafe operation of the gas valves is considered. This is because typical control systems use more power for the redundant controls to meet the failsafe operational requirements mandated by regulatory agencies.

In order to be compatible with newer, energy efficient, low power sources to which the appliance industry is being driven, and in order to meet increasingly stringent failsafe requirements, there is a need in the art for an ignition control system that allows the use of low voltage sources, e.g. batteries, thermopile, hydro generator, etc., without increasing the cost and complexity of such circuitry to unacceptable levels or reducing safety. Embodiments of the present invention provides such an ignition control circuit and method compatible with such low voltage power supplies for gas burners used in intermittent pilot and direct spark ignition systems. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

BRIEF SUMMARY OF THE INVENTION

In view of the above, embodiments of the present invention provide a new and improved ignition control system that overcomes one or more of the problems existing in the art. More particularly, embodiments of the present invention provide a new and improved ignition control system for intermittent pilot and/or direct spark ignition systems. Still more particularly, embodiments of the present invention provide a new and improved ignition control system for intermittent pilot and/or direct spark ignition systems that allow the use of low voltage sources, e.g. batteries or self-supplied voltage systems such as thermopile or hydro generators. Further, embodiments of the present invention provide a new and improved redundant ignition control system for intermittent pilot and/or direct spark ignition systems that provides failsafe operation in a low power environment.

In one embodiment of the present invention, a redundant gas valve control system and method that provides fail safe gas valve operation with minimum power consumption is provided. The system utilizes dual microprocessor technology with simplified communication techniques between the microprocessors, preferably utilizing a general purpose input output (I/O). Such an embodiment minimizes resources required by each processor and allows for use of simple, low cost components. The system minimizes power consumption by sensing the supply voltage and energizing the gas valve control coils with variable pulse width modulated (PWM) power instead of utilizing a DC voltage to activate and hold the valves. As such, the system is particularly useful in intermittent pilot or direct spark ignition systems without a standing pilot flame in low power applications, such as battery powered or self powered systems.

In one embodiment the pilot and main gas valves are controlled by three switching elements. In one embodiment each of the pilot valve and the main gas valve are controlled by a switching element under the control of the main processor. A third switching element, a gas valve supply switch under the control of the supervisory processor, controls the power to both of the main valve switch and the pilot valve switch. In one embodiment of the present invention, additional fail safe circuitry in the form of a high pass filter is interposed between the switching element and the gas valve. This high pass filter ensures that only the properly generated high frequency signal will energize the gas valves, and prevents the application of DC voltage that may be generated by a fault within the system from energizing the gas valves.

In one embodiment of the present invention, the system operates to provide low power, redundant ignition control. Such operation includes two main operating modes, to with a standby mode and a heat mode of operation. During the standby mode of operation, the main processor sleeps, and periodically awakens to check to see whether a call for heat has been issued. Preferably, the supervisory processor sleeps until the main processor determines that a call for heat has been generated.

During the heat mode, the system conducts a gas valve verification process, and upon successful completion thereof enters an ignition sequence. Once the ignition sequence has successfully ignited the burner, this embodiment enters a burner monitoring period until the call for heat expires. At such a point, the system enters a heat shut down mode of operation, and thereafter returns to the standby mode. If, at any point or during any mode of operation a fault is detected by either the main processor or the supervisory processor, the heat mode is aborted or ended and the gas control valves are turned off.

Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

FIG. 1 is a simplified single line schematic circuit diagram of one embodiment of a redundant ignition control system constructed in accordance with the teachings of the present invention; and

FIG. 2 is a simplified signal timing diagram illustrating system operation during various phases of an ignition cycle.

While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to FIG. 1, wherein is illustrated one embodiment of a low voltage ignition control system 100 for intermittent pilot and/or direct spark ignition systems utilized in gas burning appliances constructed in accordance with the teachings of the present invention. It should be noted at the outset, however, that while the following description will describe features of this embodiment as applied to an operative environment in which it finds particular applicability, such description and embodiment should be taken by way of example only, and not by way of limitation. Other embodiments of the present invention and other operative environments are within the scope of the present invention and their full scope is specifically reserved herein.

As indicated above, the ignition control system 100 provides redundant control of both a pilot gas valve 102 and a main gas control valve 104 in an intermittent pilot burner system. In a direct spark ignition system that does not include a pilot burner, the system 100 provides redundant control of the main gas control valve 104. Such redundant control ensures fail safe operation of the ignition system, which is essential for gas burning appliances to be installed in commercial facilities and consumer dwellings.

As will be discussed more fully hereinbelow, the control methodologies implemented by the ignition control system 100 also ensure that the operation thereof requires a minimum of power consumption, thereby enabling operation with low power applications. Such battery powered or self powered applications are becoming more common in intermittent pilot or direct spark ignition systems without a standing pilot flame. However, while the ignition control system 100 provides such minimum power consumption, its application to conventional powered gas burning appliances that do not require low power consumption is not inhibited thereby. That is, the ignition control system 100 of the present invention operates equally well regardless of the power availability of the source, and provides enhanced low power consumption operation in each application.

As may be seen from FIG. 1, the ignition control system 100 utilizes dual microprocessor technology, i.e., a main processor 106 and a supervisory processor 108. The ignition control system 100 also utilizes a simplified communication technique between the processors 106, 108, which minimizes resources required by each processor 106, 108 and allows for the use of simple, low cost components. The control technique utilized by the processors 106, 108 also minimizes the power consumption by sensing the supply voltage and utilizing a variable pulse width modulated (PWM) signal instead of DC voltage to energize the pilot gas valve 102 and the main gas control valve 104, and reduces the PWM duty cycle, and hence power consumption, to hold the valves 102, 104 open once actuated.

In the illustrated embodiment, the main processor 106 is programmed to provide the complete ignition control and system monitoring typical with conventional gas burning appliance controls. The supervisory processor 108 supports the fail safe operation of the system. It also monitors for the presence of flame via flame sense electrode 110 in addition to the flame sense monitoring performed by the main processor 106.

To coordinate operation between the main processor 106 and the supervisory processor 108, a single, unidirectional communication technique is employed. Specifically, the illustrated embodiment utilizes a general purpose digital I/O line 112 to provide the control signals from the main processor 106 to the supervisory processor 108. These control signals utilize a variable PWM signal to minimize the resources required by each of the two processors 106, 108. In one embodiment the main processor 106 controls the duty cycle of the PWM signal to request the supervisory processor to perform each of the different functions during the various phases of operation to be discussed more fully below in relation to FIG. 2. Alternatively, the main processor 106 controls the frequency of the signal on line 112 to request the supervisory processor 108 to perform its various functions.

The supervisory processor 108 monitors the I/O line 112 to verify that the main processor's logic or programming is operating correctly by verifying that the communications from the main processor 106 on the I/O line 112 is sequenced properly. The supervisory processor 108 also verifies that the main processor 106 is running at the correct frequency by monitoring the frequency and duty cycle of the control signal on I/O line 112.

To provide true redundant operation, the main processor also monitors various signals to deduce whether or not the supervisory processor 108 is operating properly. Specifically, the main processor monitors the gas valve supply sense input line 114 to verify that the supervisory processor 108 has received and is implementing the correct sequence command based on the signal provided on the I/O line 112. This monitoring of the gas valve supply sense input line 114 also allows the main processor 106 to verify that the supervisory processor's logic or programming is operating correctly by verifying that the signal in the gas valve supply sense input line 114 is sequenced properly under the control of the supervisory processor 108. This monitoring also allows the main processor 106 to verify that the supervisory processor 108 is running at the correct frequency. In one embodiment this is accomplished by monitoring the frequency and period of the signal on the gas valve supply sense input line 114.

This sequencing verification is dependent upon the command signal on the I/O line 112 from the main processor 106 to the supervisory processor 108. As indicated above, the various modes of operation are commanded by varying the duty cycle or frequency of the control signal on I/O line 112. Specifically, in one embodiment there are four valid states corresponding to four different operational modes of operation that may be commanded by the main processor 106.

In a standby mode of operation, the main processor 106 generates no signal on I/O line 112, or a PWM signal with zero duty cycle. This allows for minimal power consumption during the standby mode of operation, which will be described more fully hereinbelow. Upon an initial call for heat, the main processor 106 generates a gas valve verification sequence command on I/O line 112 by providing a PWM signal having a first duty cycle, e.g., a duty cycle of approximately ten percent. When the main processor 106 wishes to command the initiation of an ignition sequence, it provides a second PWM signal on I/O line 112, e.g., of approximately twenty percent, to the supervisory processor 108. When the main processor 106 desires that the supervisory processor 108 enter the burner monitoring mode of operation, it generates a third PWM signal on I/O line 112 higher than the ignition sequence duty cycle.

In one embodiment of the present invention, the ignition control system 100 provides a duty cycle of approximately thirty percent when a high power supply voltage is available, and provides a PWM signal of approximately forty percent duty cycle if the system is being powered from a low power supply voltage. This provides maximum flexibility to allow the ignition control system 100 of the present invention to be utilized in various gas burning appliances regardless of the capacity or type of the source of power, while still ensuring proper sensing of the flame sense electrode 110 to ensure reliable detection of a flame regardless of the supply voltage level.

Depending on the particular operational mode commanded by the main processor 106, the supervisory processor 108 operates to control the switching of a gas valve supply switch 116 to condition and couple the operating voltage from the appliance's power supply. Once the main processor 106 has verified that proper switching of the gas valve supply switch 116 is occurring, it then operates to close the pilot valve switch 118 to energize the pilot gas valve 102 in applications that utilize a pilot valve 102. In accordance with its sequencing programming, the main processor 106 then controls the switching of the main gas valve switch 120 to energize the main gas control valve 104 once the pilot flame has been detected by the flame sense circuitry illustrated in FIG. 1 as the flame sense electrode 110.

The gas valve supply switch 116, the pilot valve switch 118, and the main gas valve switch 120 may be implemented utilizing various technologies depending on the applicable system parameters, such as supply voltage, gas valve loads, etc. Indeed, these individual switches 116, 118, 120 may be implemented using MOSFETs, BJTs, electro-mechanical relays, or a combination of these components. Preferably, the gas valve supply switch 116 is implemented using an electronically controlled switch that is capable of generating the high frequency PWM signal utilized within the ignition control system 100 to energize the pilot gas valve 102 and the main gas control valve 104 to minimize power consumption.

This minimization of the power consumption of the ignition control system 100 is enabled by the supervisory processor 108 by recognizing that different power requirements exist for energizing and holding the pilot gas valve 102 and main gas control valve 104. As such, the supervisory processor 108 controls the gas valve supply switch 116 to initially supply a high duty cycle PWM power signal until main burner ignition has been confirmed. It will then change the switching frequency of the gas valve supply switch 116 to generate a relatively lower duty cycle PWM signal such that the power supplied to the pilot gas valve 102 and the main gas control valve 104 is just sufficient to hold the valves 102, 104 in their open state. This power requirement typically is substantially less than the power required to actually open the valves 102, 104 from their closed state. Such operations substantially reduce the power consumed by the ignition control system 100, and therefore provides a distinct advantage over prior systems.

In addition to the minimization in power consumption, the supervisory processor 108 also varies the duty cycle of the switching of the gas valve supply switch 116 based on the input power supply voltage. This provides a distinct advantage when the ignition control system 100 is utilized in a gas burning appliance having an unregulated battery voltage power supply from which to energize the gas valves 102, 104. This is because the voltage variation in such an application may be as much as two times over the life of the battery. The compensation of such wide voltage swings also serves a protection function, particularly in applications utilizing line voltage as the power supply input. This is because such line voltage often includes over voltage spikes and other conditions that might otherwise damage the system components or the valves 102, 104 themselves.

In a further embodiment the adjustment of the PWM duty cycle commanded by the supervisory processor 108 may be used to compensate for an ambient temperature variation to ensure stable gas valve operation over a wide range of ambient temperatures. The information regarding ambient temperature may be taken from the main controller thermostat for the gas burning appliance, or a separate ambient temperature sensor may be included if such information is not otherwise available.

In an embodiment wherein the supervisory processor 108 controls the switching of the gas valve supply switch 116 to generate a PWM power signal, the ignition control system 100 includes further fail safe circuitry to prevent the valves 102, 104 from opening upon a failure of the switches 116, 118, 120. As illustrated in FIG. 1, each of the power lines leading to the valves 102, 104 includes a high pass filter 122, 124. These filters 122, 124 will only pass the properly generated PWM power signal resulting from the switching of the gas valve supply switch 116 under the control of the supervisory processor 108 to the valves 102, 104. Importantly, these filters 122, 124 will block the application of DC power to the valves 102, 104, which may be generated by a failure within the control system, and thus will prevent the inadvertent energization of either of the valves 102, 104.

While the embodiment of the ignition control system 100 illustrated in FIG. 1 includes two high pass filters 122, 124 to protect against inadvertent energization of the valves 102, 104, other embodiments may not require both filters 122, 124. That is, depending on the gas valve configuration and parameters, such as in systems that include a redundant pilot and main valve, only one high pass filter is may be included. This filter 122 would typically be placed on the pilot valve output because, when such redundant valves are used, application of power to the main gas control valve 102 without energization of the pilot valve will not result in actuation of the main gas control valve.

Having described the basic structure and operation of the ignition control system 100 of an embodiment of the present invention, attention is now directed to the simplified timing diagram of FIG. 2 for a detailed discussion of the various modes of operation provided in one embodiment of the ignition control system 100. This discussion will refer to the signal traces of FIG. 2 along with the physical line on the schematic drawing of FIG. 1 to aid in an understanding of the physical system and its operation. As such, the numbering scheme employed uses one-hundred-series numbers for items appearing on FIG. 1, and two-hundred-series numbers for the signals on FIG. 2 to aid the reader in locating the appropriate item.

As discussed above, the ignition control system 100 of the present invention operates basically in two modes of operation, to with a standby mode and a heat mode. During the standby mode of operation, which is initiated and maintained when the main processor 106 determines that a heat demand is not present, the main processor 106 stops communicating with the supervisory processor 108, as illustrated by the lack of a mode control signal 200 (communicated via I/O line 112). During such a standby mode of operation, the main processor 106 also disables the pilot valve switch control signal 206 on line 126, and the main gas valve switch control signal 210 on line 130. The supervisory processor 108 also disables the gas valve supply switch control signal 202 on line 138. As a result of the disabling of the gas valve supply switch 116, the pilot valve switch 118, and the main gas valve switch 120, the gas valve supply sense signal 204 sensed via line 114, the pilot valve supply sense signal 208 sensed via line 128, the main gas valve supply sense signal 212 sensed via line 132, and the flame sense signal 214 sensed via lines 134 and 136 are also low during this standby mode of operation.

Preferably, the main processor 106 enters a sleep mode during the standby mode for a predetermined period of time. After this predetermined period, the main processor 106 wakes, performs an internal self check, and determines if a call for heat exists. If a call for heat does exist, then the main processor 106 switches to the heat mode at time T₀ illustrated in FIG. 2 as will be discussed in greater detail below. However, if a call for heat does not exist, then the main processor 106 goes back to its sleep mode for the predetermined period of time.

Once this occurs, the supervisory processor 108 will see that the mode control signal 200 on the I/O line 112 is null. In this condition the supervisory processor 108 turns off the gas valve supply switch control signal 202 on line 138 (if the signal 202 were energized), and then the supervisory processor 108 will enter a sleep mode. Unlike the main processor 106, however, the supervisory processor 108 will not wake from the sleep mode after a predetermined period of time in one embodiment, but will instead await a state change on I/O line 112 before it is awoken from its sleep mode. While such lack of communication on I/O line 112 will cause the supervisory processor 108 to disable the gas valve supply switch 116 as a means of ensuring fail safe operation in the event of failure of main processor 106, in an alternate embodiment the main processor 106 will generate a different duty cycle PWM signal on I/O line 112 to request the supervisory processor 108 to turn off the gas valve supply switch 116 and enter its sleep mode.

When the main processor 106 determines that a call for heat is present, indicated in FIG. 2 at time T₀, the main processor 106 generates a PWM mode control signal 200 on I/O line 112 to start the gas valve verification sequence mode of operation. During this gas valve verification sequence, both the main processor 106 and the supervisory processor 108 verify, by sensing the flame sense signal 214 on lines 134 and 136 that flame is not present. If flame is sensed during the gas valve verification sequence, the ignition control system 100 will enter a fail safe mode of operation.

If, however, no flame is present during this initial check, the supervisory processor 108 will then begin controlling the switching of the gas valve supply switch 116 by generating the gas valve supply switch control signal 202 on line 138. As illustrated, this initial gas valve supply switch control signal at time T₀ is a low frequency or low duty cycle PWM signal. The main processor 106 then senses the gas valve supply sense signal 204 on line 114 to verify the supervisory processor 108 timing. Thereafter, the supervisory processor 108 changes the gas valve supply switch control signal 202 to a DC output on line 138 to close the gas valve supply switch 116. The main processor 106 then senses line 114 to ensure that the gas valve supply sense signal 204 reflects the DC signal present when the gas valve supply switch 116 is closed.

During this operation the main processor 106 also checks the pilot valve supply sense signal 208 on line 128 and the main gas valve supply sense signal 212 on line 132 to ensure that no voltage is present on these lines when neither the pilot valve switch control signal 206 on line 126 or the main gas valve switch control signal 210 on line 130 is present. Once the supervisory processor 108 has closed the gas valve supply switch 116 to generate the DC voltage, the main processor 106 then sequences the pilot valve switch control signal 206 to close the pilot valve switch 118 and then verifies that the pilot valve supply sense signal 208 on line 128 is present. The main processor 106 then disables the pilot valve switch control signal 206 and verifies that the pilot valve supply sense signal 208 also drops low. The main processor 106 then energizes the main gas valve switch control signal 210 on line 130 to close the main gas valve switch 120, and verifies that the main gas valve supply sense signal 212 reflects the DC level on line 132.

This pilot valve switch 118 and main gas valve switch 120 cycling is performed during the DC voltage generation of the closed gas valve supply switch 116 without affect on the pilot gas valve 102 or the main gas control valve 104 in view of the inclusion of the capacitive high pass filters 122, 124 which blocks the application of such a DC signal to the pilot gas valve 102 or the main gas control valve 104. In embodiments that do not utilize such additional circuitry, this check is not performed. Instead, the operational status of the pilot valve switch 118 and the main gas valve switch 120 is either verified upon its initial attempt to close these switches 118, 120, or the supervisory processor 108 controls the switching duty cycle of the gas valve supply switch 116 to a very low level that is insufficient to open valves 102, 104 and the checking is performed during such switching.

Once the gas valve verification sequence has been completed, the main processor 106 then changes the duty cycle of the mode control signal 200, as illustrated at time T₁, to initiate the ignition sequence mode of operation. As a result of this change in duty cycle of the mode control switch 200, the supervisory processor 108 generates a high duty cycle PWM gas valve supply switch control signal 202 to the gas valve supply switch 116 via line 138. This is done to begin generation of a supply voltage sufficient to energize the pilot gas valve 102 and the main gas control valve 104. The main processor 106 then turns on the pilot valve switch control signal 206 to close the pilot valve switch 118, and begins a trial for ignition period. As may be seen from the pilot valve supply sense signal 208, the high duty cycle PWM signal generated by the switching of the gas valve supply switch 116 will then be applied through the high pass filter 122 to the pilot gas valve 102 to allow gaseous fuel to flow to the pilot for ignition. Once the flame sense signal 214 indicates the presence of a pilot flame, the main processor 106 then generates the main gas valve switch control signal 210 on line 130 to close the main gas valve switch 120. Once the main gas valve switch 120 is closed, the high duty cycle PWM signal generated by the switching of the gas valve supply switch 116 will be applied through the high pass filter 124 to energize the main gas control valve 104.

Once this initial ignition sequence has been completed, the main processor 106 changes the duty cycle of the mode control signal 200 on line 112 to institute the monitor burner mode of operation at time T₂. In this monitor burner mode of operation the supervisory processor 108 changes the duty cycle of the gas valve supply switch control signal 202 to a low duty cycle to reduce the power consumption of the system commensurate with the holding power requirements of the pilot gas valve 102 and main gas control valve 104, as opposed to the higher power requirements to initially actuate these valves.

This low duty cycle gas valve supply switch control signal 202 is continuously generated until the main processor 106 determines that the call for heat is satisfied. At this point, indicated at time T₃, the main processor 106 de-energizes the pilot valve switch control signal 206 and the main gas valve switch control signal 210 to shut off the pilot gas valve 102 and the main gas control valve 104. The main processor 106 also disables the mode control signal 200 on line 112. As a result, the supervisory processor 108 disables the gas valve supply switch control signal 202 to open the gas valve supply switch 116 once the supervisory processor 108 realizes that the mode control signal 200 has been disabled. This period between the main processor 106 disabling the mode control signal 200 and the actual loss of flame at time T₄ is the heat shut down period, the duration of which may vary based upon the actual plumbing of the gas appliance's fuel delivery system.

During the entire heat mode of operation, the main processor 106 continuously monitors the state of the gas valve supply sense signal 204, the pilot valve supply sense signal 208, and the main gas valve supply sense signal 212. If the main processor 106 senses any invalid signal on any of these inputs, the main processor 106 will then de-energize the pilot valve switch 118 and the main gas valve switch 120, and will disable the mode control signal 200 to send the supervisory processor 108 into the heat shut down mode of operation. As discussed above, during the heat shut down sequence the supervisory processor 108 will de-energize the gas valve supply switch 116 and enter the sleep mode until a change of state of the mode control signal 200 on I/O line 112 is sensed by the supervisory processor 108.

All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 

1. A ignition control system for use with intermittent pilot systems for gas burners having a pilot gas valve and a main gas control valve, comprising: a main processor; a supervisory processor; a gas valve supply switch controllably coupled to the supervisory processor, the gas valve supply switch having a power input and a gas valve supply output; a pilot valve switch controllably coupled to the main processor, the pilot valve switch having a first gas valve supply input coupled to the gas valve supply output and a pilot valve power output; a main gas valve switch controllably coupled to the main processor, the main gas valve switch having a second gas valve supply input coupled to the gas valve supply output and a main gas control valve power output; and wherein the main processor is configured to generate a pulse width modulated mode control signal to control operation of the supervisory processor, the main processor further configured to sense the gas valve supply output to verify proper operation of the supervisory processor.
 2. The ignition control system of claim 1, wherein the main processor is configured to generate a pulse width modulated mode control signal of a first duty cycle to cause the supervisory processor to enter a gas valve verification mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal to cause the gas valve supply switch begin a switching sequence, and wherein the main processor is further configured to monitor the gas valve supply output to verify proper operation of the supervisory processor.
 3. The ignition control system of claim 2, further comprising a pilot gas valve high pass filter coupled to the pilot valve power output, and wherein the supervisory processor is configured to turn on the gas valve supply switch control signal to close the gas valve supply switch, and wherein the main processor is configured to generate a pilot valve switch control signal to close the pilot valve switch, the main processor further configured to monitor the pilot valve power output to ensure proper operation of the pilot valve switch.
 4. The ignition control system of claim 3, wherein the main processor is configured to generate a main gas valve switch control signal to close the main gas valve switch, the main processor further configured to monitor the main gas control valve power output to ensure proper operation of the main gas control valve switch.
 5. The ignition control system of claim 4, further comprising a main gas control valve high pass filter coupled to the main gas control valve power output.
 6. The ignition control system of claim 2, further comprising a flame sense circuit, and wherein at least one of the main processor and the supervisory processor is configured to monitor the flame sense circuit during the gas valve verification mode of operation.
 7. The ignition control system of claim 6, wherein both of the main processor and the supervisory processor are configured to monitor the flame sense circuit during the gas valve verification mode of operation.
 8. The ignition control system of claim 1, wherein the main processor is configured to generate a pulse width modulated mode control signal of a second duty cycle to cause the supervisory processor to enter an ignition sequence mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a high duty cycle to cause the gas valve supply switch begin a high power switching sequence, and wherein the main processor is further configured to generate a pilot valve switch control signal to close the pilot valve switch.
 9. The ignition control system of claim 8, further comprising a flame sense circuit, and wherein the main processor is configured to monitor the flame sense circuit during the ignition sequence mode of operation and, upon verification of the presence of flame, to generate a main gas valve switch control signal to close the main gas valve switch.
 10. The ignition control system of claim 8, further comprising a flame sense circuit, and wherein at least one of the main processor and the supervisory processor is configured to monitor the flame sense circuit during a trial for ignition period, and wherein at least one of the main processor and the supervisory processor disables at least the gas valve supply switch control signal when no flame is sensed during the trial for ignition period.
 11. The ignition control system of claim 9, wherein the main processor is configured to generate a pulse width modulated mode control signal of a third duty cycle to cause the supervisory processor to enter monitor burner mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a low duty cycle to cause the gas valve supply switch begin a low power switching sequence.
 12. The ignition control system of claim 11, wherein the main processor is configured to disable the mode control signal once a call for heat is removed, and wherein the supervisory processor is configured to disable the gas valve supply switch control signal to close the gas valve supply switch.
 13. A ignition control system for use with direct spark systems for gas burners having a main gas control valve, comprising: a main processor; a supervisory processor; a gas valve supply switch controllably coupled to the supervisory processor, the gas valve supply switch having a power input and a gas valve supply output; a main gas valve switch controllably coupled to the main processor, the main gas valve switch having a gas valve supply input coupled to the gas valve supply output and a main gas control valve power output; and wherein the main processor is configured to generate a pulse width modulated mode control signal to control operation of the supervisory processor, the main processor further configured to sense the gas valve supply output to verify proper operation of the supervisory processor.
 14. The ignition control system of claim 13, wherein the main processor is configured to generate a pulse width modulated mode control signal of a first duty cycle to cause the supervisory processor to enter a gas valve verification mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal to cause the gas valve supply switch begin a switching sequence, and wherein the main processor is further configured to monitor the gas valve supply output to verify proper operation of the supervisory processor.
 15. The ignition control system of claim 14, further comprising a high pass filter coupled to the gas valve supply output, and wherein the supervisory processor is configured to turn on the gas valve supply switch control signal to close the gas valve supply switch, and wherein the main processor is configured to generate a main gas valve switch control signal to close the main gas valve switch, the main processor further configured to monitor the main gas control valve power output to ensure proper operation of the main gas control valve switch.
 16. The ignition control system of claim 14, further comprising a flame sense circuit, and wherein both of the main processor and the supervisory processor are configured to monitor the flame sense circuit during the gas valve verification mode of operation.
 17. The ignition control system of claim 13, wherein the main processor is configured to generate a pulse width modulated mode control signal of a second duty cycle to cause the supervisory processor to enter an ignition sequence mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a high duty cycle to cause the gas valve supply switch begin a high power switching sequence, and wherein the main processor is further configured to generate a main gas valve switch control signal to close the main gas valve switch.
 18. The ignition control system of claim 17, further comprising a flame sense circuit, and wherein at least one of the main processor and the supervisory processor is configured to monitor the flame sense circuit during a trial for ignition period, and wherein at least one of the main processor and the supervisory processor disables at least the gas valve supply switch control signal when no flame is sensed during the trial for ignition period.
 19. The ignition control system of claim 17, wherein the main processor is configured to generate a pulse width modulated mode control signal of a third duty cycle to cause the supervisory processor to enter monitor burner mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a low duty cycle to cause the gas valve supply switch begin a low power switching sequence.
 20. The ignition control system of claim 19, wherein the main processor is configured to disable the mode control signal once a call for heat is removed, and wherein the supervisory processor is configured to disable the gas valve supply switch control signal to close the gas valve supply switch. 